1. Field of the Invention
This invention relates to a deposition detecting apparatus which automatically detects the deposition of an electromagnetic contactor, a relay, an inverter or the like (hereinafter referred to as "electromagnetic contactor") and which opens an electric circuit in accordance with the detected electromagnetic contactor deposition.
2. Description of the Prior Art
High-tension heavy current is used for driving the motors of large processing machines, such as hoist cranes. Therefore, in opening and closing a driving circuit for a motor, etc., a push-button switch is used for remote-controlling an electromagnetic contactor or a similar switch. However, the life the electromagnetic contacts depends upon the frequency of use, values of tension and current, etc. Especially in three-phase power sources, when any one of the three phases has a bad connection, only the other two phases are connected to the load resulting in the so-called single-phase running which can cause damage, and when contacts of the electromagnetic contactor become fused together, "runaway" running results which can cause much damage to both persons and objects.
In view of the above, the Japanese Utility Model Registration Application Laying Open Gazette No. 63-121337, for example, disclosed a circuit for detecting the deposition (fusing together) of contacts of a relay using a sequence circuit.
In the above conventional contact deposition detecting apparatus for an electromagnetic contactor, an electric circuit of the apparatus is in parallel with a driving circuit. Therefore, a driving current flows in the electric circuit and it is difficult to electrically separate them from each other. Thus, when the detecting apparatus has malfunctioned, it has bad influence upon the driving circuit. With this in mind, it has been the practice to set a permissible time for usage of each electromagnetic contactor and to change contactors with new ones after their use for this permissible time. This, however, involves un-economical use of contactors because some are still safely usable at the time of change.